This Invention relates to a method and device for converting heat energy into electricity and refrigeration by the use of materials near their Ferromagnetic or Ferroelectric phase transition point; the electro-calorific and magneto-calorific effects or Ferrofluids, Ferro-electric Fluids or Liquid Crystals by non-Carnot and Carnot limited thermodynamic cycles.
Direct conversion of heat into electricity with minimal moving parts is desirable, and electricity is probably the most versatile manifestation of motive power. There are many schemes and devices for directly converting heat into electricity by thermo-couples, Seebeck and Peltier devices. An example of such a device employing the magneto-calorific effect is disclosed in U.S. Pat. No. 5,714,829.
U.S. Pat. No. 4,3912,356 discloses a method of controlling the temperature of an element, and the magnetic field applied thereto, to cause the temperature-magnetism state of the element to traverse a loop. The loop may have a first portion of concurrent substantially isothermal or constant temperature and increasing applied magnetic field, a second portion of lowering temperature and constant applied magnetic field, a third portion of isothermal and decreasing applied magnetic field, and a fourth portion of increasing temperature and constant applied magnetic field.
U.S. Pat. No. 3,073,974 discloses a method of employing a capacitive element having differences in specific heat capacity between the charged and uncharged conditions over a given temperature range, for converting between thermal and electrical energy, comprising the steps of applying electrical energy to the element at a given voltage within the given temperature range to change the specific heat capacity from an uncharged value to a charged value, subjecting the element to a source of thermal energy to vary the temperature of the clement within the temperature range while maintaining the element in the charged condition; extracting electrical energy from the element at a voltage different from the voltage within the temperature range to change the specific heat capacity of the element from a charged value to an uncharged value; and cooling the element to effect a change in the thermal energy of the element, thereby varying the temperature of the element within the given temperature range while maintaining the element in an uncharged condition.
All of these schemes operate between two reservoirs-source and sink, and as such they are Carnot cycle limited. Low efficiency is a problem in these devices when dealing with low enthalpy reservoirs such as ocean heat. It is an object of the present invention to seek to provide a thermodynamic cycle and method that alleviates this difficulty.
Accordingly, an aspect of the present invention provides an apparatus for performing a thermodynamic cycle comprising: a sample having a ferrormagnetic phase transition temperature; means to magnetise the sample above the ferromagnetic phase transition temperature of the sample; and means to cool the sample to a temperature that is below the ferromagnetic phase transition temperature thereof, wherein the demagnetisation of the sample whilst the sample is below the ferromagnetic phase transition temperature thereof causes the generation of an independent magnetic flux, and wherein the means to magnetise the sample comprises a co-material provided adjacent the sample, the co-material exhibiting a phase transition when a predetermined action is performed thereon, the apparatus further comprising means to perform the action on the co-material.
Advantageously, the means to perform the predetermined action comprises means to apply an electrostatic field to the co-material.
Alternatively, the means to perform the predetermined action comprise means to tension the co-material.
Preferably, the phase transition exhibited by the co-material is a second-order phase transition.
Another aspect of the present invention provides an apparatus for performing a thermodynamic cycle, comprising: a sample that exhibits temporary magnetic remanence; and means to magnetise the sample within a time period that is less than one tenth of the duration of the cycle, the duration of the cycle being less than one ten thousandth of a second, wherein demagnetisation of the sample causes the generation of an independent magnetic flux.
Conveniently, the sample cools during a first portion of the demagnetisation thereof.
Advantageously, the temperature of the sample increases during a second portion of the demagnetisation thereof.
Preferably, the apparatus further comprises means to convert at least some of the independent magnetic flux into an electric current.
Conveniently, the sample is of a first permeability, and wherein a quantity of a material having a second permeability is provided adjacent the sample, the first permeability being lower than the second permeability.
A further aspect of the present invention provides an apparatus for performing a thermodynamic cycle comprising: a sample having a ferroelectric phase transition temperature; means to polarise the orientation of electric dipoles in the sample at a temperature above the ferroelectric phase transition temperature; means to cool the sample to a temperature that is below the ferroelectric phase transition temperature thereof, wherein depolarisation of the sample whilst the sample is below the ferroelectric phase transition temperature thereof during the depolarisation thereof causes the generation of an independent electric flux.
Advantageously, the electrocalorific effect associated with the polarisation of the sample heats the sample during polarisation thereof.
Preferably, the sample is at an initial ambient temperature thereof prior to the polarisation thereof.
Conveniently, the means to cool the sample to a temperature that is below the ferroelectric phase transition temperature thereof comprise, at least partially, a heat exchange between the sample and ambient surroundings thereof.
Advantageously, the sample is heated to the ambient temperature during the depolarisation thereof.
Preferably, the means to cool the sample to a temperature that is below the ferroelectric phase transition temperature thereof comprise, at least partially, an inverse electrocalorific effect associated with part of the depolarisation of the sample.
Another aspect of the present invention provides an apparatus for performing a thermodynamic cycle, comprising: a sample that exhibits temporary electric remanence; and means to polarise the sample within a time period that is less than one tenth of the duration of the cycle, the duration of the cycle being less than one ten thousandth of a second, wherein the depolarisation of the sample causes the generation of an independent electric flux.
Conveniently, the sample cools during a first portion of the depolarisation thereof.
Advantageously, the temperature of the sample increases during a second portion of the depolarisation thereof.
Preferably, the means to polarise the sample comprises a flow of electric current.
Alternatively, the means to polarise the sample comprises at least one rotating permanent magnet.
Conveniently, the apparatus further comprises means to convert at least some of the independent electric flux into an electric current.
Advantageously, the sample is of a first permittivity and a quantity of a material having a second permittivity is provided adjacent the sample, the first permittivity being lower than the second permittivity.
A further aspect of the present invention provides a method of converting energy, comprising the steps of: providing a sample having a ferromagnetic transition temperature; magnetising the sample while the sample is above the ferromagnetic transition temperature thereof; allowing the sample to demagnetise while the sample is below the ferromagnetic transition temperature thereof, the demagnetisation of the sample causing an independent magnetic flux; and converting at least some of the independent magnetic flux into an electric current.
Advantageously, the method further comprises the step of maintaining an ambient temperature in the region of the sample that is higher than the ferromagnetic transition temperature thereof.
Preferably, the method further comprises the step of allowing the sample to cool to the ambient temperature following the magnetisation thereof.
Another aspect of the present invention provides a method of convening energy, comprising the steps of: providing a sample that exhibits temporary magnetic remenance; magnetising the sample, thereby causing the sample to become magnetised in a time period that is less than one tenth of the duration of the cycle, the duration of the cycle being less than one ten thousandth of a second; allowing the sample to demagnetise, the demagnetisation of the sample causing an independent magnetic flux; and converting at least some of the independent magnetic flux into an electric current.
Conveniently, the step of providing a sample comprises the step of providing a ferrofluid.
Advantageously, the step of providing a sample comprises the steps of providing a sample having a first permeability, and further providing a quantity of a material having a second permeability adjacent the sample, the first permeability being higher than the second permeability.
Preferably, at least one rotating permanent magnet magnetises the sample.
Advantageously, a carrier operable to carry a flow of electric current therethrough magnetises the sample.
Conveniently, the step of magnetising the sample comprises the steps of providing a co-material adjacent the sample, which co-material exhibits a further phase transition when a predetermined action is performed thereon, and providing means to perform the action on the co-material.
Advantageously, the step of providing means to perform the action on the co-material comprises providing means to apply an electrostatic field to the co-material.
Alternatively, the step of providing means to perform the action on the co-material comprises providing means to apply tension to the co-material.
Advantageously, the magnetising step and the converting step are carried out by a single means operable to magnetise the sample and to convert at least some of the independent magnetic flux into an electric current.
A further aspect of the present invention provides a method of converting energy, comprising the steps of: providing a sample having a ferroelectric transition temperature; polarising the orientation of electric dipoles in the sample while the sample is above the ferroelectric transition temperature thereof; allowing the sample to depolarise while the sample is below the ferroelectric transition temperature thereof, the depolarisation of the sample causing an independent electric flux; and converting at least some of the independent electric flux into an electric current.
Preferably, the method further comprises the step of maintaining an ambient temperature in the region of the sample that is higher than the ferroelectric transition temperature thereof.
Conveniently, the method further comprises the step of allowing the sample to cool to the ambient temperature following the polarisation thereof.
Another aspect of the present invention provides a method of converting energy, comprising the steps of: providing a sample that exhibits temporary electric remenance; polarising the orientation of electric dipoles in the sample in a time period that is less than one tenth of the duration of the cycle, the duration of the cycle being less than one ten thousandth of a second; allowing the sample to depolarise, the depolarisation of the sample causing an independent electric flux; and converting at least some of the independent electric flux into an electric current.
Advantageously, the step of providing a sample comprises the step of providing a ferro-electric-fluid.
Preferably, the step of providing a sample comprises the steps of providing a sample having a first permittivity, and further providing a quantity of a material having a second permittivity adjacent the sample, the first permittivity being lower than the second permittivity.
Conveniently, at least one rotating permanent magnet polarises the sample.
Alternatively, a carrier operable to carry a flow of electric current therethrough polarises the sample.
Advantageously, the polarising step and the converting step are carried out by a single means operable to polarise the sample and to convert at least some of the independent electric flux into an electric current.
Preferably, the method further comprises the step of providing a circulation system comprising micro-encapsulated material whose melting point is close to an operational temperature range of the sample.
A further aspect of the present invention provides a method of generating electricity according to any of the above methods.
A further aspect of the present invention provides a method of producing an electric current according to any of the above methods.